Wiktor Wise
Thermal failure of electrical components refers to the degradation and breakdown of electronic devices due to high temperatures and repeated temperature oscillations. According to a study by the US Air Force Avionics Integrity Program, elevated temperatures account for over 50% of electronic equipment failures, with vibration and humidity contributing to an additional 20%. Thermal cycling, or the repeated fluctuation of temperatures during the lifetime of a device, can lead to solder fatigue and cracking, impairing the heat transfer capabilities of the components and ultimately resulting in thermal runaway, melting, fires, or even explosions.
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What You'll Learn
Thermal cycling
The occurrence of thermal cycling leads to stress generation due to the mismatch in thermal properties between the substrate materials and any surface oxidation product. This can cause mechanical failure of a protective surface layer, leading to accelerated degradation of the substrate material and a shortened life of the component. For example, the power-handling ability of a resistor may be greatly reduced when applied in high-altitude aircraft.
In the context of electronic components, thermal cycling can induce solder fatigue, causing the bonds between components and circuit boards to deform, crack, or break. This can lead to electrical failure. Thermal cycling can also affect the mechanical performance of restorations by straining the composite material and restored structures, as well as their bonded interface.
To prevent thermal cycling-induced failures, engineers should aim to reduce thermal stressors in the design stage. Thermal cycling is a vital step in product testing and development, helping to ensure the long-term performance and reliability of electronic devices.
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Thermal runaway
The cycle occurs in an electrical circuit in conditions of undissipated high temperature, which leads to a reduction in the component's electrical resistance, which further leads to an increase in current, which again leads to an increase in temperature. This process can lead to a vicious circle or positive feedback effect, causing failure, sometimes in a spectacular fashion, such as an electrical explosion or fire. Thermal runaway can also cause sudden failures, including melting, fire, or explosions.
To prevent thermal runaway, well-designed electronic systems typically incorporate current-limiting protection, such as thermal fuses, circuit breakers, or PTC current limiters. Additionally, design considerations regarding spacing and ventilation must be taken into account to ensure that components can withstand the anticipated conditions.
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Soldering issues
Soldering is a fundamental skill in electronic circuit design, but it can also cause thermal failure of electrical components. Soldering heat damage can occur due to various reasons, including:
Prolonged exposure to excessive heat
Overheating can lead to solder joint cracking, compromising connections and affecting the overall functionality of the electronic device. It may also result in the degradation of insulation materials, causing short circuits or other electrical issues.
Incorrect soldering iron temperature and poor soldering technique
Using the wrong tip size, temperature, or duration, applying too much or too little solder, or moving the iron or the component while soldering can all lead to soldering heat damage.
Inadequate tools and equipment
Using a cheap or defective soldering iron, a dirty or worn-out tip, low-quality or incompatible solder, or lacking proper accessories like a stand, sponge, flux, or heat sink can affect the quality and efficiency of soldering. This can lead to issues such as uneven heat distribution, oxidation, corrosion, or thermal stress, which can cause cracks, warping, or delamination of the board or component.
Unsuitable environment and conditions
Working in a poorly ventilated, humid, dusty, or noisy area, or exposing the circuit to direct sunlight, moisture, or static electricity can interfere with the soldering process. This can lead to condensation, contamination, or electrostatic discharge, causing potential damage to the circuit.
To prevent thermal failure of electrical components due to soldering issues, it is essential to address these factors and ensure proper soldering techniques, tools, and environmental conditions are in place.
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Component materials
The thermal failure of electrical components can occur due to a range of reasons, and the choice of component materials plays a crucial role in preventing such failures. Firstly, it is important to understand that different materials have different coefficients of thermal expansion (CTE). When materials with mismatched CTEs are used together, such as in soldered joints, thermal cycling can lead to solder fatigue and cracking, compromising the integrity of the electrical connections.
To mitigate this, engineers should carefully select materials with compatible CTEs to reduce thermal stressors during the design stage. This is particularly important for layered materials used to relay electricity within circuit boards, as they expand, shrink, and deform with the passage of electricity, and their response to thermal cycling is critical for accurate life testing. Additionally, the number of material layers and their arrangement can influence thermal performance.
The type of material used also affects the thermal sensitivity of electrical components. For example, liquid and electrolytic capacitors are known to fail faster at higher operating temperatures due to pressure build-up and leakage. Similarly, the lifetime of film capacitors is highly sensitive to variations in voltage and temperature. On the other hand, transistors can operate reliably for extended periods at a constant temperature, even with continual heating and cooling.
The enclosure materials and surface area further impact the thermal management of electrical components. Non-metallic and painted metallic enclosures have different heat dissipation characteristics. Larger enclosures dissipate more heat, and darker enclosures absorb more heat than lighter-coloured ones. Additionally, enclosures exposed to direct sunlight will absorb and retain more heat, affecting the components inside.
Furthermore, the presence of certain substances can accelerate thermal degradation. For instance, ionic contaminants like alkali metals and halogens can migrate from packaging materials to semiconductor dies, causing corrosion and deterioration. Humidity and aggressive chemicals can also contribute to corrosion and damage, leading to electrical failures. Therefore, the choice of packaging materials and their resistance to environmental factors are crucial in preventing thermal-related failures.
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Environmental factors
Electronic components are susceptible to environmental factors that can lead to thermal failure. High temperatures are a significant contributor to the failure of electrical components. A study by the US Air Force Avionics Integrity Program found that elevated temperatures cause over 50% of electronic equipment failures. The study also predicted that temperatures in many regions would be hotter than usual, emphasising the need for effective thermal management of electrical components to prevent productivity losses.
The impact of temperature is not limited to external heat but also includes sustained heat within the components themselves. Constantly high temperatures, even without overheating, reduce the expected lifespan of computer parts. For example, electrolytic capacitors inherently degrade over time, and this process is accelerated by heat. Similarly, transistors have been found to exhibit increased failure rates at higher temperatures.
Thermal cycling, the repeated oscillation between temperatures over the lifetime of an electronic device, is another critical environmental factor. It can lead to solder fatigue and joint failure, causing cracks and deformation in the bonds between components and circuit boards. This is due to the unique coefficient of thermal expansion (CTE) of each material, which results in mismatches in expansion and contraction rates during thermal cycling.
In addition to temperature, vibration and humidity are also significant environmental factors contributing to electronic component failures. According to the USAF study, vibration and humidity account for 40% of electronics failures. Managing heat inside enclosures can be challenging due to the detrimental effects of traditional cooling methods on vibration and humidity levels. For example, refrigerant-based air conditioners increase vibration, and fans push humid air through the enclosure.
Other environmental factors include dust, moisture, and insects, which can cause problems when they come into contact with electronic components. Dust can insulate components, disrupting airflow and contributing to moisture retention. Combined with dust, moisture can create conductive residues, leading to electrical shorts. Insects, such as ants or mosquitoes, can infiltrate electronic devices in hot and humid environments, causing unexpected issues. Therefore, regular cleaning, pest control, and storing electronics in cool, dry places are essential preventive measures.
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Frequently asked questions
Thermal failure of electrical components is when high temperatures cause damage to the circuit board, leading to product failure.
Thermal cycling, the repeated oscillation between temperatures over the lifetime of an electronic device, can cause thermal failure. High temperatures, vibration, and humidity are also common causes.
Every material has a unique coefficient of thermal expansion (CTE). When materials with different CTEs are used together, it can lead to solder fatigue and deformation, crack formation, and other types of damage.
Signs of thermal failure include discoloration or delamination of the PCB, visible damage under a high-power microscope, and secondary overvoltage damage.
Thermal failure can be prevented by using electronic devices in climate-controlled areas, avoiding high-temperature settings, and regular cleaning and pest control to keep electronics in cool, dry places.
